Hospitals have made slow progress in meeting the Institute of Medicine's patient safety goals, and implementation of safety systems has been inconsistent. The next logical question is this: What organizational characteristics predict greater implementation of patient safety systems, in terms of both extent of systems and progress over time? To answer this question, a survey was administered to 107 hospitals at two points in time. Data were consolidated into seven latent variables measuring progress in specific areas. Using the overall measure, Joint Commission-accredited hospitals showed statistically significant improvement, as reflected in the sum score (p = .01); nonaccredited hospitals did not show statistically significant improvement (p = .21). Joint Commission accreditation was the key predictor of patient safety system implementation. Management type and urban/rural status were secondary predictors. Several factors may account for the strong association between accreditation and patient safety system implementation. In 2003, the Joint Commission began tying accreditation to patient safety goals. Also, Joint Commission data are now widely available to the public and may stimulate hospitals to address safety issues. Healthcare executives, hospital trustees, regulators, and policymakers should encourage Joint Commission accreditation and reward hospital efforts toward meeting Joint Commission standards. The Joint Commission should continually strive to maintain evidence-based and state-of-the-art standards that advance the aim of providing the best possible care for hospitalized patients.